Wave guide for improving light sensor angular response

ABSTRACT

Electronic displays encounter visibility issues due to varying ambient light conditions. An ambient light sensor can be provided to sense ambient light and dynamically adjust display brightness to compensate for changes in ambient light. A wave guide for improving angular response in a light sensor is provided.

FIELD

The present specification relates generally to light sensors and moreparticularly relates to a wave guide for improving angular response in alight sensor.

BACKGROUND

Flat panel displays such as liquid crystal displays (LCD) are nowcommonplace in portable electronic devices, computers, televisions,cellular telephones, and in other display applications. Ambient lightconditions, however, can dramatically impact the displaycharacteristics, resulting in poor display visibility. To compensate forvarying ambient light conditions, and to take opportunities to reducepower consumption, ambient light sensors may be included in thedisplays. Such ambient light sensors attempt to detect the amount ofambient light and provide input to control circuitry which canautomatically adjust the brightness of the display, according to theamount of sensed ambient light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric representation of a display assembly.

FIG. 2 is a schematic cross-sectional representation of the light sensorof the assembly of FIG. 1, the cross-section being taken along thedashed-lines indicated as 2-2 in FIG. 1.

FIG. 3 shows the window, wave guide and photodetector of FIG. 2 ingreater detail.

FIG. 4 shows an idealized response curve of the intensity of light thatreaches the sensor of FIG. 3 as a result of the configuration of thewave guide of FIG. 3.

FIG. 5 shows a first exemplary configuration of the wave guide of FIG.3.

FIG. 6 shows a second exemplary configuration of the wave guide of FIG.3.

FIG. 7 shows a third exemplary configuration of the wave guide of FIG.3.

FIG. 8 shows a fourth exemplary configuration of the wave guide of FIG.3.

FIG. 9 shows a plurality of further response curves.

FIG. 10 shows a light sensor assembly as a variation on the assembly ofFIG. 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

An aspect of this specification provides a display assembly comprising:a display; a light sensor module mounted proximally to said display; acontroller connected to said light sensor module and configured toreceive an electronic signal representing a measurement of ambient lightincident on said display; said controller connected to said display andconfigured to adjust brightness of said display based on said electronicsignal; said light sensor module comprising a window for transmittingambient light; a light sensor for receiving said ambient light andconfigured to generate said electronic signal; a wave guide comprising atextured surface disposed between said window and said light sensor;said textured surface having a geometric structure; said geometricstructure configured according to a material and a thicknesses of saidwindow; said geometric structure further configured to guide ambientlight travelling through said window onto said light sensor such that anintensity of ambient light that strikes said sensor varies substantiallyproportionally according to a function comprising a cosine of an angleof incidence of ambient light striking said window.

The geometric structure can be further configured such that said ambientlight strikes said sensor at an angle that is substantially normal tosaid sensor regardless of said angle of incidence.

The display assembly can further comprise a substrate; said texturedsurface applied to said substrate; said substrate for mechanicallyaffixing said wave guide to said window. The substrate can be affixedvia an adhesive. The geometric structure can be further configuredaccording to a material and thickness of said substrate.

The textured surface can be integrally formed into said window.

The textured surface can comprise a plurality of bosses.

The bosses can be trapeziums, partial-spheroids, or four-sided pyramids.

The bosses can be regularly spaced, or irregularly spaced.

The textured surface can be made from one of polymethyl methacrylate,polyethylene terephthalate, acrylic, or epoxy.

The wave guide can be made from a material having a refractive index ofbetween about 1.4 and about 1.7.

The light sensor module can further comprise a light emitter configuredto emit light at a first angle; said wave guide configured to scatterlight emitted from said light emitter out of said window at angle widerthan said first angle.

The display assembly can be configured for incorporation into a portableelectronic device and said light emitter is configured to indicate astatus of said portable electronic device.

Another aspect of the specification provides a light sensor moduleaccording to any of the foregoing.

Another aspect of the specification provides a wave guide according toany of the foregoing.

Referring now to FIG. 1, a display assembly is indicated generally at50. Display assembly 50 comprises a display 54, a light sensor module58, and a controller 62. Display assembly 50 can be incorporated intoany electronic apparatus having a display, including but not limited toportable electronic devices, computers, televisions, cellulartelephones, desktop telephones, and major appliances.

Display 54 comprises one or more light emitters such as an array oflight emitting diodes (LED), liquid crystals, plasma cells, or organiclight emitting diodes (OLED). Other types of light emitters arecontemplated. Such light emitters, when activated by controller 62,produce emitted light, as indicated by the arrows labeled “EL” in theFigures. Emitted light EL is shown as being emitted substantiallynormally from the surface of display 54, although the actual viewingrange can be much wider.

Display 54 is also subject to incident ambient light AL. In FIG. 1,ambient light AL is shown as incident in a direction that issubstantially normal to the surface of display 54. Those skilled in theart will appreciate that ambient light AL can reduce the visibility ofemitted light EL. Controller 62 is therefore configured to receive anelectrical signal from sensor module 58 representing an intensity ofambient light AL and to adjust the brightness of emitted light EL tocompensate for reduced visibility of emitted light EL due to ambientlight AL. As will be discussed further below, display assembly 50 isconfigured to respond to ambient light AL that is incident from a rangeof different angles.

As best seen in FIG. 2, light sensor module 58 comprises a light sensoror other type of photodetector 66 that is configured to convert ambientlight AL that is incident on photodetector 66 into an electrical signalES. Electrical signal ES has a voltage or other electricalcharacteristic that is generally proportional to the intensity(expressed as, for example, in units of lux) of ambient light AL thatlands on photodetector 66. Electrical signal ES is received atcontroller 62 which is configured to brighten or dim display 54accordingly.

Light sensor module 58 also comprises a housing 70 and a cover 74.Housing 70 comprises a chassis 72 that is shaped so as to define a lighttransmissive chamber 78, and photodetector 66 is disposed within the endof chamber 78 that is opposite to cover 74. Chamber 78, in a presentembodiment, contains air and is therefore transmissive of ambient lightEL.

Cover 74 comprises a frame 76 that overlays chassis 72. Frame 72 is alsoshaped to define a window 82. A wave guide 86 is disposed within chamber78 between window 82 and photodetector 66. In a present embodiment, waveguide 86 abuts window 82. As will be discussed in greater detail below,wave guide 86 can be a separate item from window 82, or wave guide 86can be integrally formed into window 82.

Chassis 72 and frame 76 are substantially mechanical in function andtherefore can be of any suitable material to achieve the desiredmechanical characteristics of the corresponding display assembly 50application. For example, where display assembly 58 is part of a displayin a portable electronic device, chassis 72 and frame 76 will be madefrom materials and dimensioned to be rugged enough to mechanicallysupport window 82, wave guide 86 and photodetector 66, within lightsensor module 58, and also be rugged enough to withstand dropping orother types of physical blows to which a portable electronic device canbe commonly subjected.

By the same token, window 82, wave guide 86, chamber 78 andphotodetector 66 are substantially optical in function, (or in the caseof photodetector 66, electro-optical), and as will be discussed furtherbelow, are therefore selected from materials that provide the desiredoptical, (or electro-optical) characteristics. Again, within the contextof display assembly 58 being used within a portable electronic device,window 82, wave guide 86 and photodetector 66 are also configured toprovide a certain degree of mechanical ruggedness, again so that theentire display assembly 50 can withstanding the physical blows to whicha portable electronic device can be commonly subjected.

As will be discussed further below, wave guide 86 can be physicallyintegrated into window 82, or each can be separate items which aremechanically affixed to each other (e.g. via an adhesive) at the time ofassembly.

FIG. 3 shows an embodiment of window 82, wave guide 86 and photodetector86 in greater detail. In FIG. 3, wave guide 86 includes a substrate 88and a textured surface 90. FIG. 3 also shows two separate representativebeams of ambient light AL-1, and AL-2.

Ambient light AL-1 is shown as incident at an angle Al1 that is normalto the surface of window 82. Angle Al1 is assigned the variable ⊖1 inFIG. 3, where ⊖1 equals ninety degrees. Ambient light AL-1 is also shownas having intensity I1 when ambient light I1 strikes the surface ofwindow 82. Intensity I1 is assigned the variable X in FIG. 3. I1 can beexpressed in units of lux. For purposes of explaining this embodiment, Xcan be any value associated with ambient light conditions.

Ambient light AL-2 is shown as incident at an angle Al2 that is lessthan ninety degrees to the surface of window 82. Angle Al2 is assignedthe variable ⊖2 in FIG. 3. Ambient light AL-2 is also shown as havingintensity I2 when ambient light I2 strikes the surface of window 82. Forpurposes of explaining this embodiment, I2 is deemed to equal I1, andtherefore I1=X.

Window 82 can be characterized in terms of its material with anassociated index of refraction n1, and having a particular thickness T1.The index of refraction n1 of window 82 is represented in FIG. 3 by thechange in angle of ambient light AL-2 as ambient light AL-2 travelsthrough window 82.

Substrate 88 can be also characterized in terms of its material with anassociated index of refraction n2, and having a particular thickness T2.The index of refraction n2 of substrate 88 is represented in FIG. 3 bythe change in angle of ambient light AL-2 as ambient light AL-2 travelsthrough substrate 88.

What is not represented in FIG. 3, but will occur to those of skill inthe art, are the reflections at the junctions between different adjacentmaterials. Thus, a certain amount of ambient light AL-1 will beinternally reflected as ambient light AL-1 enters and exits window 82,and enters and exits substrate 88, and enters and exits textured surface90. Accordingly, in an actual implementation, the actual intensity ofambient light AL-1 and ambient light AL-2 entering chamber 78 will beless than intensity I1 and intensity I2 due to attenuation and lossesresulting from passing through window 82 and wave guide 86. Suchattenuation is not represented in FIG. 3 for purposes of simplifyingexplanation.

Textured surface 90 is defined by a three-dimensional geometricstructure that is configured based on the materials and thicknesses ofwindow 82 and substrate 88, such that the intensity of ambient lightthat strikes photodetector 66 varies substantially proportionally to thecosine of the angle of incidence of the ambient light striking window82. Additionally, the three-dimensional geometric structure of texturedsurface 90 is configured such that ambient light strikes photodetector66 at an angle that is substantially normal to photodetector 66,regardless of the angle that the ambient light actually strikes window82.

(It should now be apparent that in certain configurations, texturedsurface 90 can be integrally formed with window 82, thereby obviatingthe need for substrate 88. In this configuration, the same principles asthe previous paragraph apply, except that only the material andthickness of window 82 need be considered.)

In FIG. 3, the intensity of ambient light AL that strikes the surface ofsenor 66 is represented by the variable Y. Thus, in mathematical terms,the geometric structure of textured surface is configured according thefollowing function:

Y=I(cos(Al))   Function 1:

Where:

Y is the intensity of ambient light that strikes the surface ofphotodetector 66

I is the intensity of light that strikes the surface of window 82

Al is the angle of incidence of light as it strikes the surface ofwindow 82.

A graph of plotting Function 1, where I=1, is shown in FIG. 4.

Various materials for wave guide 86 are contemplated, includingpolycarbonate, polymethyl methacrylate, polyethylene terephthalate,acrylic, and epoxy. As desired for a particular configuration, suchmaterials can also be used for window 82.

Presently, any material can be chosen that has suitable mechanicalproperties and has a refractive index of between about 1.4 and about1.7.

Presently, textured surface 90 is configured for range of the visibleelectro-magnetic spectrum, and certain wavelengths at the periphery ofthat spectrum, specifically wavelengths of between about 350 nanometersand about 900 nanometers.

FIG. 5 shows a non-limiting exemplary embodiment of a specific geometricstructure for textured surface 90, although in FIG. 5 the texturedsurface of this specific embodiment is indicated at reference 90A,within a specific wave guide 86A. Textured surface 90A is thus comprisedof a plurality of bosses in the form of trapeziums 94A. While FIG. 5shows each trapezium 94A as aligned, in variations the trapeziums can beirregularly aligned.

The thickness of textured surface 90A is, in the present embodiment,between about 0.001 millimeters and about five millimeters, and thematerial for textured surface 90A can be polycarbonate, polymethylmethacrylate, polyethylene terephthalate, acrylic, or epoxy. In apresent embodiment substrate 88A is integral with window 82A. In thepresent embodiment, substrate 88A is etched directly onto window 82A.Substrate 88A has a thickness of about 0.05 millimeters to about twomillimeters. Window 82A has a thickness of about 0.1 millimeters toabout five millimeters. Table I shows the various dimensions for eachtrapezium 94A.

TABLE I Dimensions for Trapezium 94A Dimension reference Type DimensionUnit Tolerance  98A Angle 48 Degree +/−12  100A Length 0.01 mm +5/−0.01104A Radius 0.01 mm +0.5/−0.01   108A Length 0.05 mm +5/−0.04

FIG. 6 shows another non-limiting exemplary embodiment of anotherspecific geometric structure for textured surface 90, although in FIG. 6the textured surface of this specific embodiment is indicated atreference 90B, within a specific wave guide 86B. Textured surface 90B isthus comprised of a plurality of bosses in the form of partial-spheroids94B. While FIG. 6 shows each semi-spheroid 94B as aligned, in variationsthe partial-spheroids 94B can be irregularly aligned.

The thickness of textured surface 90B is, in the present embodiment,between about 0.001 millimeters and about five millimeters, and thematerial for textured surface 90B can be polycarbonate, polymethylmethacrylate, polyethylene terephthalate, acrylic, or epoxy. In apresent embodiment substrate 88B is integral with window 82B. In thepresent embodiment, substrate 88B is etched directly onto window 82B.Substrate 88B has a thickness of about 0.05 millimeters to about twomillimeters. Window 82B has a thickness of about 0.1 millimeters toabout five millimeters. Table II shows the various dimensions for eachpartial-spheroid 94B.

TABLE II Dimensions for Partial-Spheroid 94B Dimension reference TypeDimension Unit Tolerance  98B Angle 44.91 Degrees +/−15  100B Length0.03 mm +5/−0.03 104B Radius 0.01 mm +5/−0.01

FIG. 7 shows another non-limiting exemplary embodiment of anotherspecific geometric structure for textured surface 90, although in FIG. 7the textured surface of this specific embodiment is indicated atreference 90C, within a specific wave guide 86C. Textured surface 90C isthus comprised of a plurality of bosses in the form of four-sidedpyramids 94C. While FIG. 7 shows each four-sided pyramid 94C as aligned,in variations the four-sided pyramids 94C can be irregularly aligned.

The thickness of textured surface 90C is, in the present embodiment,between about 0.001 millimeters and about five millimeters, and thematerial for textured surface 90B can be polycarbonate, polymethylmethacrylate, polyethylene terephthalate, acrylic, or epoxy. In apresent embodiment substrate 88C is integral with window 82C. In thepresent embodiment, substrate 88C is etched directly onto window 82C.Substrate 88C has a thickness of about 0.05 millimeters to about twomillimeters. Window 82C has a thickness of about 0.1 millimeters toabout five millimeters. Table III shows the various dimensions for eachfour-sided pyramid 94C.

TABLE III Dimensions for Four-Sided pyramids 94C Dimension referenceType Dimension Unit Tolerance  98C Angle 75 Degrees +15/−15 100C Length0.018 millimeters    +5/−0.015 104C Length 0.015 millimeters   +5/−0.015 (between each pyramid) 108C Radius Zero millimeters  +/−2

FIG. 8 shows another non-limiting exemplary embodiment of anotherspecific geometric structure for textured surface 90, although in FIG. 8the textured surface of this specific embodiment is indicated atreference 90D, within a specific wave guide 86D. Textured surface 90D isthus comprised of a plurality of bosses in the form of four-sidedpyramids 94D. While FIG. 8 shows each four-sided pyramid 94D as aligned,in variations the four-sided pyramids 94C can be irregularly aligned.

The thickness of textured surface 90D is, in the present embodiment,between about 0.001 millimeters and about five millimeters, and thematerial for textured surface 90D can be polycarbonate, polymethylmethacrylate, polyethylene terephthalate, acrylic, or epoxy. In apresent embodiment substrate 88D is integral with window 82D. In thepresent embodiment, substrate 88D is etched directly onto window 82D.Substrate 88D has a thickness of about 0.05 millimeters to about twomillimeters. Window 82D has a thickness of about 0.1 millimeters toabout five millimeters. Table IV shows the various dimensions for eachfour-sided pyramid 94D.

TABLE IV Dimensions for Four-Sided pyramids 94D Dimension reference TypeDimension Unit Tolerance  98D Angle 86 Degrees +/−10  100D Length 0.03millimeters +5/−0.03 104D Length 0.02 millimeters +5/−0.02 (between eachpyramid) 108D Radius 0.015 millimeters  +2/−0.015

It is to be understood that Function 1 in FIG. 4 is an idealized targetprofile for Y (where Y varies to Intensity I and Angle of Incidence Al)in the establishment of a configuration of textured surface 90. Theactual function that can result in relation to a particular geometricstructure of textured surface 90 has a range of acceptable deviationfrom Function 1, such that in certain embodiments the geometricstructure of textured surface 90 results in a profile that substantiallyconforms with Function 1, without exactly matching Function 1. FIG. 9shows a variety of different curves to illustrate. In FIG. 9, curve 150is the curve that corresponds with Function 1 and as shown in FIG. 4.Curve 154 shows the response curve associated with textured surface forfour-sided pyramid 94C when ambient light AL is incident along the planeshown in FIG. 3. Curve 158 shows the response curve associated withtextured surface for four-sided pyramid 94C when ambient light isincident along the plane that is normal to the plane shown in FIG. 3.

Again recall that curve 150 is the curve that corresponds with Function1 and as shown in FIG. 4. Ranges of design tolerances for curve 150 arealso proposed herein, including curve 162 shows an exemplary uppertolerance boundary for design specifications for the geometric structureof textured surface 90, while curve 166 shows an exemplary lowertolerance boundary for design specifications the geometric structure oftextured surface 90. Presently, an upper tolerance from Function 1 canbe about positive five percent (+5%) a lower tolerance from Function 1can be about negative five percent (−5%).

Curve 170 shows a measured response for a prior art device that does notinclude wave guide 86. The prior art device is a BlackBerry Bold™ fromResearch in Motion Inc., of Waterloo, Ontario Canada.

Variations the foregoing are contemplated. For example, chamber 78 canbe a vacuum or filled with a light transmissive medium. However,adjustments to wave guide 86 will be made to accommodate the index ofrefraction and other optical characteristics whatever medium is usedwithin chamber 78. As another example the means by which light sensormodule 58 incorporates wave guide 86 is not particularly limited. Forexample, wave guide 86 can be produced as a separate item that isaffixed to window 82. Alternatively, textured surface 90 can be formeddirectly on the surface of window 82 that is nearest to chamber 78,thereby obviating the need for substrate 88 altogether.

A still further variation is shown in FIG. 10, which shows a lightsensor module 58E. Light sensor module 58E includes many of the samecomponents of light sensor module 58, and accordingly like elements bearlike references, except followed by the suffix “E”. However, in lightsensor module 58E, photodetector 66E is reduced in size to allow for alight emitter such as a light emitting diode (LED) 200E. Light sensormodule 58E can be incorporated into a portable electronic device whereLED 200E can be used as an indicator light. The indicator light can beused, for example, to indicate a low battery condition of the device.Other functions for the indicator light are contemplated. For example,where the portable electronic device includes wireless telephony oremail messaging capability, then LED 200E can be used to indicate thepresence of a wireless network. LED 200E can also be of the type that isconfigured to generate multiple colours. In module 58E, wave guide 86Ehas two functions: first to direct ambient light onto photodetector 66Eas previously discussed, and second to help scatter light emitted fromLED 200E out of window 82E across a wider range of angles.

While certain specific embodiments have been discussed herein,combinations, subsets and variations of those embodiments arecontemplated. It is the claims attached hereto that define the scope oftime-limited exclusive privilege of this specification.

1. A display assembly comprising: a display; a light sensor modulemounted proximally to said display; a controller connected to said lightsensor module and configured to receive an electronic signalrepresenting a measurement of ambient light incident on said display;said controller connected to said display and configured to adjustbrightness of said display based on said electronic signal; said lightsensor module comprising: a window for transmitting ambient light; alight sensor for receiving said ambient light and configured to generatesaid electronic signal; a wave guide comprising a textured surfacedisposed between said window and said light sensor; said texturedsurface having a geometric structure; said geometric structureconfigured according to a material and a thicknesses of said window;said geometric structure further configured to guide ambient lighttravelling through said window onto said light sensor such that anintensity of ambient light that strikes said sensor varies substantiallyproportionally according to a function comprising a cosine of an angleof incidence of ambient light striking said window.
 2. The displayassembly of claim 1 wherein said geometric structure is furtherconfigured such that said ambient light strikes said sensor at an anglethat is substantially normal to said sensor regardless of said angle ofincidence.
 3. The display assembly of claim 1 further comprising asubstrate; said textured surface applied to said substrate; saidsubstrate for mechanically affixing said wave guide to said window. 4.The display assembly of claim 3 wherein said substrate is affixed via anadhesive.
 5. The display assembly of claim 3 wherein said geometricstructure is further configured according to a material and thickness ofsaid substrate.
 6. The display assembly of claim 1 wherein said texturedsurface is integrally formed into said window.
 7. The display assemblyof claim 1 wherein said textured surface comprises a plurality ofbosses.
 8. The display assembly of claim 7 wherein said bosses aretrapeziums.
 9. The display assembly of claim 7 wherein said bosses arepartial-spheroids.
 10. The display assembly of claim 7 wherein saidbosses are four-sided pyramids.
 11. The display assembly of claim 7wherein the bosses are regularly spaced.
 12. The display assembly ofclaim 7 wherein the bosses are irregularly spaced.
 13. The displayassembly of claim 1 wherein said textured surface is made from one ofpolymethyl methacrylate, polyethylene terephthalate, acrylic, or epoxy.14. The display assembly of claim 1 wherein said wave guide is made froma material having a refractive index of between about 1.4 and about 1.7.15. The display assembly of claim 1 wherein said function has a lowertolerance of about −5%.
 16. The display assembly of claim 1 wherein saidfunction has an upper tolerance of about +5%.
 17. The display assemblyof claim 1 wherein said light sensor module further comprises a lightemitter configured to emit light at a first angle; said wave guideconfigured to scatter light emitted from said light emitter out of saidwindow at angle wider than said first angle.
 18. The display assembly ofclaim 17 wherein said display assembly is configured for incorporationinto a portable electronic device and said light emitter is configuredto indicate a status of said portable electronic device.
 19. A lightsensor module comprising: a window for transmitting ambient light; alight sensor for receiving said ambient light; a wave guide comprising:a textured surface disposed between said window and said light sensor;said textured surface having a geometric structure; said geometricstructure configured according to a material and a thicknesses of saidwindow; said geometric structure further configured to guide ambientlight travelling through said window onto said light sensor such that anintensity of ambient light that strikes said sensor varies substantiallyproportionally according to a function comprising a cosine of an angleof incidence of ambient light striking said window.
 20. A wave guidecomprising: a textured surface for positioning between a window and alight sensor; said textured surface having a geometric structure; saidgeometric structure configured according to a material and a thicknessesof said window; said geometric structure further configured to guideambient light travelling through said window onto said light sensor suchthat an intensity of ambient light that strikes said sensor variessubstantially proportionally according to a function comprising a cosineof an angle of incidence of ambient light striking said window.